The development of new drugs is expensive, risky, and often takes years. An alternative that is increasingly appealing is repurposing of existing drugs to diseases other than those that they are licenced for [1]}, [2]}, [3]}.
There are also many compounds that have been developed through pharmaceutical research that failed at some point in the development process but may be appropriate for another condition. An example is Viagra that was originally being developed for treating angina but had a side-effect that subsequently became its key selling point.
